Syria announced during United Nations climate talks on Tuesday that it would sign the Paris agreement on climate change. The move, which comes on the heels of Nicaragua signing the accord last month, will leave the United States as the only country that has rejected the global pact.

According to several people who were in a plenary session at the climate talks in Bonn, Germany, a Syrian delegate announced that the country was poised to send its ratification of the Paris agreement to the United Nations.

“This is the very last country that actually announced, so everyone has joined and the U.S. is now so isolated,” said Safa Al Jayoussi, executive director of IndyAct, an environmental organization based in Lebanon that works with Arab countries on climate change.

A White House spokeswoman, Kelly Love, pointed reporters to a statement the administration made when Nicaragua joined the pact, noting there had been no change in the United States’ position.

“As the president previously stated, the United States is withdrawing unless we can re-enter on terms the are more favorable for our country,” the statement said.

President Trump announced in a Rose Garden speech this summer that the United States would quit the deal, calling it bad for America’s economy.

The Paris agreement, struck in 2015 under former President Barack Obama, calls on nearly 200 countries to voluntarily curb greenhouse gas emissions. At the time, only Nicaragua and Syria did not join, for very different reasons.

Nicaraguan leaders argued that the deal did not go far enough toward keeping carbon emissions at safe levels and helping vulnerable countries protect themselves from the effects of climate change. But last month Daniel Ortega, Nicaragua’s president, and Rosario Murillo, his vice president and wife, said in a joint statement that the country would sign anyway. “The Paris agreement, despite not being the ideal agreement, is the only instrument that currently allows this unity of intentions and efforts,” they said.

Syria has been mired in a civil war since 2011. And because the Syrian government is subject to European and American sanctions, its leaders had been unable to send representatives abroad to negotiate or sign the pact.

Roua Shurbaji, a spokeswoman at the Syrian mission to the United Nations, said the country’s decision was part of an effort “to be effective in all international areas including climate change.”

Syria has not yet submitted targets for cutting greenhouse gases. Syria produces only a tiny fraction of global emissions, but every country that is party to the accord, including poverty-stricken and war-torn nations and tiny islands, has produced a plan for cutting carbon output.

“We will get there,” Ms. Shurbaji said. “We are in the process of becoming part of the agreement. We will have our commitments and targets.”

“With Syria’s decision, the relentless commitment of the global community to deliver on Paris is more evident than ever,” said Paula Caballero, director of the climate change program at the World Resources Institute. “The U.S.’s stark isolation should give Trump reason to reconsider his ill-advised announcement and join the rest of the world in tackling climate change.”

Under the rules of the Paris agreement, the United States cannot formally withdraw until late 2020. Until then, administration officials have said, they will continue to negotiate the terms of the deal, but they have not specified what changes would be sufficient for the United States to reconsider quitting. American negotiators are attending the talks underway in Germany.

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